How to detect steghid malware in image files

Does anyone have a good method for detecting malware in image files? I have heard of methods such as changing the file extension, for example change a .jpg file to a .pdf, but I am not able to find anymore information on this method.

I mainly just want a reliable source for desktop wallpapers, but I don’t trust any of these wallpaper sites, or google images haha.

Thank you in advance!